1. Field of the Invention
This invention relates to a multispeed transducer system; and, more particularly, to a position indicating system having both a coarse and fine position transducer for indicating position over a large range.
2. Description of the Prior Art
In order to provide information over a multiple number of revolutions or electrical cycles and to know precisely which revolution or cycle is being monitored, a multispeed transducer system must be employed. In a two speed transducer system, a fine transducer is used for indicating the position of the instrumented shaft within the revolution being observed and a coarse transducer is provided to determine which revolution or cycle is being checked.
Two speed transducer systems are well known in the art. They have been widely used to provide electrical instrumentation for the determination of the position of a rotary shaft in applications where information is needed as to absolute shaft position over multiple revolutions. A typical system wherein the positions sensors are resolvers consists of two resolvers mechanically interconnected by a speed reducer. The rotary shaft to be instrumented can be directly coupled to the fine resolver to mechanically provide input angle data representing the angular position of the shaft. The fine resolver, which is directly coupled to the shaft, is used to provide electrical signals over any given single revolution of the shaft indicating the angular orientation with a high degree of accuracy. By an appropriate gear reduction mechanism or by the differential reduction technique, as described more fully in copending CSR application Ser. No. 504,431, the coarse resolver is caused to provide electrical signals which indicate the total number of revolutions of the shaft being instrumented. The combination of the fine resolver and coarse resolver can thus provide electrical signals indicating the absolute position of the instrumented shaft over multiple revolutions. The outputs of the coarse and fine resolvers can then be converted to a digital word.
It has been recognized in the prior art, for example, when the fine resolver data is a three-digit binary coded decimal word and the coarse resolver position is also a three-digit binary coded decimal word, the coarse signal can be made to overlap the fine by one full decade. That is, the least significant decade of the fine signal. This overlap allows for good synchronization between the coarse and the fine position word. However, as is common, a slight error or variation can occur between the coarse digital output and the fine digital output. This error can cause an ambiguity around the point at which the fine transducer completes a cycle. For example, for a three-decade binary coded decimal word, an ambiguity can exist near the point where the fine digital word changes from 999 to 000. When the fine digital word is combined with the coarse digital word, this small position error can result in a gross combined readout error. For proper operating, it is desirable that the combined output signal provide nonambiguous error free indications at all times.
When the term resolver is used herein it is intended to include: synchro, induction potentiometer, resolver, transmitter, control transformer, differential control transformer and any other sinusoidal position transducer.